1. Field of the Invention
The present invention relates in general to next generation technology for fabricating electrical interconnects in integrated circuit devices, and relates in particular to a method and apparatus for filling micro-cavities formed on a surface of a substrate with metal plating.
2. Description of the Related Art
Aluminum is a typical material used for fabricating conductor circuit patterns in integrated semiconductor devices. An aluminum conductor line pattern is fabricated by first sputtering an aluminum film on a semiconductor wafer (wafer), followed by forming circuit patterns on the aluminum film by means of photolithography, and etching off unwanted regions to complete the conductor line pattern. As the devices become more highly integrated, there have been increasing demands for a finer conductor line pattern. Referring to FIGS. 27A-27C, to meet such demands for micro-fabrication, the width of grooves 303 and contact hole 301 for producing conductor line 311 and plug 313 must be made smaller, typically in a range of 0.13 to 0.18 xcexcm. When the width of the conductor line becomes so narrow, aluminum begins to show problems due to its inferior properties.
To other types of metals than aluminum, the above-described conventional method of circuit fabrication is sometimes difficult to apply, and therefore, a damascene process has been performed by fabricating stud holes and wiring cavities on a circuit board first, and then filling the cavities with a suitable metal by using processes such as chemical vapor deposition (CVD), sputtering or plating, and finishing the circuit board by chemical mechanical polishing (CMP) to complete conductor line fabrication.
Plating has been used widely for forming metallic films and has many advantages. FIG. 28 shows a setup for conventional plating. A plating chamber 1 contains a plating solution 9 in which are immersed a cathode 3, having a substrate W, and an opposing anode 4, and the plating solution 9 is stirred with a stirrer 11 during plating.
Compared to other processes, the plating cost is relatively low, high purity products can be produced, and processes can be done at a relatively low temperature to avoid degrading thermal effects. However, it is difficult to use plating to fill micro-cavities C such as grooves 303 and contact holes 301 without leaving some internal voids. When a substrate W having micro-cavities C is immersed in plating solution 9, it is not unusual to have residual air remaining inside the cavities C, and it is not possible to infiltrate the cavities C completely with the plating solution 9. This is considered to be due to the effects of wettability of the substrate W and the surface tension force of plating solution 9, and, especially for such shapes as the contact hole 301, which is deeper than it is wide (for example, an aspect ratio, depth/width, of about 5), air tends to remain in the cavity much more frequently. Similarly, it becomes much more difficult to displace spent liquid of plating solution 9 with fresh plating solution containing active metallic ions. This difficulty increases as the width of the cavities C becomes narrower.
It is an object of the present invention to provide a method and an apparatus for plating to enable a high quality metallic deposit to be produced inside the micro-cavities formed on a surface of a substrate, such as a semiconductor wafer, by completely infiltrating the micro-cavities with a plating solution and refreshing the plating solution in the micro-cavities during plating.
The present invention is to establish such an object by a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprising: immersing the substrate in a liquid held in a processing chamber; evacuating the processing chamber so as to remove residual bubbles from the micro-cavities and to degas the liquid within the micro-cavities; and subjecting the liquid to boiling in at least those regions adjacent to the substrate.
Accordingly, after removing the gas dissolved in the liquid or residual bubbles from the micro-cavities utilizing a phenomenon of nucleate boiling, the plating solution is infiltrated into the cavities so that metal can be plated inside of the cavities to efficiently produce a high quality deposit which is free of internal defects. This process is basically applicable to both electro- and electroless-plating processes.
The liquid may comprise a plating solution so that plating can be readily performed. In another option, a preferred liquid other than a plating solutions which is more easily introducible to the micro-cavities is usable. Such liquid may include water, alcohol or another suitable liquid. In this case, replacing or diluting the liquid with a plating solution may be necessary prior to plating.
The processing chamber may be a plating chamber so that the plating process can be done without transferring the substrate. In another option, the processing chamber may be made as a pre-plating processing chamber only for the pre-plating process.
In the boiling step, interior chamber pressure may be reduced to a value less than a saturated vapor pressure of the liquid. This will lower the boiling point of the liquid so that there is no need to raise the temperature of the liquid to a high temperature, thus resulting in an energy efficient and productive plating process. In the boiling step, the substrate may be heated from a back surface of the substrate. This will promote selective heating of those regions close to the cavities so that expelling of bubbles from the cavities and boiling in the cavities are enhanced. In the boiling step, interior chamber pressure may be reduced and at the same time, the substrate may be heated from the back surface.
Between a degassing step and a boiling step, interior chamber pressure may be raised to a high pressure. Also, boiling and pressurizing may be repeatedly carried out. These steps will enable the solution to reliably infiltrate the cavities, and to replace the solution inside the cavities periodically with fresh solution, thereby realizing defect-free plating.
It is also permissible to perform a boiling step while plating. Boiling may be carried out intermittently or continuously. This will enable to carry out plating while exchanging old plating solution inside the cavities with fresh plating solution to efficiently carry out the process of depositing metal in the cavities.
In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises a sealable processing chamber; an evacuating device for reducing interior chamber pressure; and a gas inlet device for pressurizing the chamber interior. The evacuating device is capable of selectively reducing interior chamber pressure to at least two pressure values, one being less than a saturated vapor pressure of the liquid, and the other being an intermediate value between the saturated vapor pressure and atmospheric pressure.
In this apparatus, liquid such as plating solution in the chamber, air, dissolved gas or gas bubbles in the plating solution, and bubbles attaching to the substrate can be made to undergo volume change or changes in their liquid state, so that liquid may be infiltrated into the cavities and/or the old solution may be refreshed with new solution. This will permit to form a metal deposit within the cavities efficiently by plating, without creating internal defects in the deposited metal. A heating device to heat the plating solution may be provided to facilitate the liquid filtration or to raise plating efficiency.
The evacuating device may have an exhaust pipe to connect a vacuum pump for reducing interior chamber pressure, and the exhaust pipe may be provided with a shutoff valve and a control valve for adjusting flow resistance. This will permit the system to be switched between two vacuum levels: a pressure intermediate between one atmosphere and the saturated vapor pressure; and a saturated vapor pressure or lower. Such a switching operation will enhance degassing of dissolved gas in the liquid by reduced pressure and expelling bubbles from the cavities by volume expansion on the one hand, and vapor release due to nucleate boiling in the cavities prompted by a high vacuum.
The evacuating device may have a vacuum pump to reduce interior chamber pressure and two parallel exhaust pipings having different flow resistance to connect the vacuum pump to the plating chamber.
The apparatus may be provided with a heating device for heating the substrate through a back surface of the substrate.
The apparatus may be provided with a vibrator means for stirring the plating solution in the plating chamber. These are all effective means for promoting liquid boiling in the cavities.
In another aspect of the invention, a method for fabricating wiring on a substrate comprises: immersing the substrate in a liquid in a processing chamber; evacuating the processing chamber so as to remove residual bubbles from the micro-cavities and to degas the liquid within the micro-cavities; subjecting the liquid to boiling in at least those regions adjacent to the substrate; plating the substrate so as to produce a metal deposit inside the micro-cavities; and removing unwanted portions of metal deposit formed in the micro-cavities by polishing using chemical and mechanical polishing methods.
The liquid may be a plating solution so that plating can be readily performed, or, a preferred liquid other than a plating solution easily introducible to the micro-cavities. In this case, a step for replacing or diluting the liquid with a plating solution is necessary between the boiling and plating steps.
In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: a sealable processing chamber; a vacuum device for reducing interior chamber pressure; a substrate holder for holding the substrate in such a way that a back surface side of the substrate is liquid-tight in the processing chamber; and a heater provided internally in the substrate holder for heating the substrate.
In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: placing the substrate in a sealable processing chamber; evacuating the interior of the chamber; immersing the substrate in a liquid; and pressurizing the liquid surrounding the substrate.
Accordingly, after exhausting the non-condensable gases such as air from the surface of the substrate, a liquid is introduced into the chamber at normal temperature and pressure, and when the substrate is immersed in the liquid, the surface of the substrate touches the liquid. Although the cavities may contain bubbles formed by a vapor of the liquid because of surface tension effects, the application of pressure will destroy the bubbles and replace the cavities with infiltrated liquid.
The method may include a step of providing a pressure variation to the liquid surrounding the substrate. This will further enhance infiltration of liquid into the cavities. Such liquid may include water, alcohol or a plating solution or a mixture thereof. Selection is made by considering wettability of the substrate by the liquid and compatibility with the plating process to follow.
In the immersing step, a surface active agent may be used to improve wettability of the substrate. This will enhance wettability and facilitate infiltration of liquid into the cavities. Such agents may be added to the liquid beforehand, but the agent itself may be introduced first into the chamber to improve the wettability of the cavity surface, and then the liquid may be infiltrated into the cavities.
In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises a sealable processing chamber; a vacuum exhaust passage for evacuating the processing chamber; a liquid inlet passage for supplying a liquid to the processing chamber; a gas inlet passage for pressurizing the liquid in the processing chamber; and a gas discharge passage for discharging gas from the processing chamber.
Substrates may be processed in a group or one at a time. A liquid draining passage is useful to facilitate the processing steps. The apparatus may be shared for both pre-plating treatment and plating processes. A plurality of liquid inlet passages may be provided to enable introducing different types of liquids or surfactants continuously or concurrently.
The apparatus may be provided with a pressure varying device to produce pressure changes in the processing chamber. The pressure varying device may be a shutoff valve or a switching valve provided on at least one of the gas inlet passage or the degassing passage.
The pressure varying device may be an ultrasonic vibrator device.
In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: placing the substrate in a sealable processing chamber; charging the processing chamber with a condensable gas; and cooling the substrate to a temperature lower than a dew point of the condensable gas to form droplets thereof within the micro-cavities.
This will allow droplets to form on the surface of the cavities and attach to the inside of the cavities. Therefore, by immersing the substrate in this condition, the plating solution replaces the droplets and infiltrates the cavities by affiliating with the droplets of the condensable gas.
The method may include a step of vibrating the substrate. Cooling the substrate to below the dew point of the condensable gas does not always produce droplets. This is because the condensable gas may be in a supercooled state and remain in the gaseous state. The degree of supercooling temperature is not a constant value, and it can sometimes reach a very high value. Therefore, by vibrating the substrate, the supercooled condition of the gas inside the cavities is disturbed, thereby releasing the gas from the supercooled state and reliably forming droplets inside the cavities.
In the charging step, the charging pressure of the condensable gas may be varied. This will permit replacing the residual bubbles in the cavities with condensable gas and reliabiltity forming droplets by cooling. The environment may be evacuated first and then filled with a condensable gas so as to facilitate replacement of the residual gas in the cavities with condensable gas and to reliably form droplets by cooling.
The method may include a step of immersing the substrate in a liquid. In this case, the liquid may be degassed by subjecting the liquid to boiling or evacuating so as to avoid a formation of bubbles from the dissolved air in the liquid. The liquid for immersing the substrate is preferably a liquid having a smaller surface tension than water so as to reliably infiltrate the cavities with the liquid. The liquid may be a plating solution, then the pre-treatment process may be continued into a plating process.
In another aspect of the invention, an apparatus for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: a sealable processing chamber; a gas inlet device for introducing a condensable gas into the processing chamber; a substrate cooling device for cooling the substrate; and a liquid supply device for supplying a liquid into the processing chamber.
This apparatus enables forming droplets on the inside surfaces of the cavities and condensing continuously. Further, a vacuum device may be provided to evacuate the processing chamber. Using this apparatus, residual gas in the cavities may be replaced with a condensable gas, and by cooling, droplets can be reliably formed in the cavities. Further, a gas inlet device may be provided to pressurize the processing chamber, thereby enabling reliable infiltration of the cavities with the liquid.
A method for producing a metal deposit inside micro-cavities fabricated on a substrate, comprises heating the substrate while exposing the micro-cavities to a liquid so as to expand and expel residual bubbles from the micro-cavities to thereby infiltrate the micro-cavities with the liquid.
In this case, a heating step may be accompanied by a cyclic pressure variation in a range above atmospheric pressure such that pressurizing and returning to atmospheric pressure are repeated.
The liquid may be first pressurized during the heating step and then is returned to atmospheric pressure to thereby facilitate expelling of the residual bubbles from the micro-cavities. The liquid may be a plating solution.
In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: disposing the substrate in a pressure vessel so that both surfaces of the substrate are under an identical pressure; evacuating the pressure vessel so as to expel residual bubbles from the micro-cavities; and introducing a liquid in the pressure vessel and applying a pressure so as to infiltrate the liquid into the micro-cavities.
In another aspect of the invention, a method for producing a metal deposit inside micro-cavities fabricated on a substrate comprises: disposing the substrate in a pressure vessel so that both surfaces of the substrate are under an identical pressure; charging the pressure vessel with a gas having a solubility in a liquid; introducing the liquid into the pressure vessel; and pressurizing the liquid so as to forcibly dissolve residual bubbles of the gas in the micro-cavities into the liquid to thereby infiltrate the liquid into the micro-cavities.